A conventional alignment apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-229759. FIG. 9 is a perspective view of an X-Y stage as this conventional alignment apparatus. A platen 42 has a reference surface 43 for supporting stage devices such as an X stage 32 and Y stage 37. A fixed Y guide 38 is fixed to the platen 42 and has a side surface as a reference surface. The Y stage 37 as a moving member is guided by the fixed Y guide 38 and moved in the Y direction by a Y linear motor 41. The Y linear motor 41 includes a Y linear motor stator 39 and Y linear motor movable element 40. The X stage 32 has an X linear motor movable element (not shown), and is guided in the X direction by an X guide 33 formed on the Y stage 37. The X stage 32 is given a driving force in the X direction by an X linear motor stator 34 formed on the Y stage 37.
As shown in FIG. 9, a top plate 31 mounted on the X stage 32 can be formed into the shape of a plate. On the top plate 31, an X-direction mirror 45 and Y-direction mirror 46 for measuring positions in the X and Y directions, respectively, are mounted. The X- and Y-direction mirrors 44 and 46 are irradiated with laser beams to measure positions in the X and Y directions, respectively, on the basis of the reflected light. The conventional X-Y stage may also be moved in the Z direction parallel to the exposure light path and in directions (θx,θy,θz) around the X, Y, and Z axes by sing a θZT driving mechanism 200 shown in FIG. 11.
FIG. 10 is a view showing the state in which the θZT driving mechanism 200 shown in FIG. 11 is removed from the conventional X-Y stage. The θZT driving mechanism 200 is mounted on the upper surface of an X-stage top plate 51a of an X stage 51. An X-stage bottom plate 51c of the X stage 51 is guided by air by an air pad (not shown). Therefore, the X stage 51 can move in the X and Y directions without causing any friction on the surface of a platen 55. The driving force for moving the stage 51 in the X direction is generated by a linear motor placed on a beam 54b of a Y stage 54. A stator 51d of this linear motor has a coil. A magnet as a movable element of the linear motor is attached to the lower surface of the top plate 51a of the X stage 51. Accordingly, when an electric current is allowed to flow through the coil, the magnet generates a driving force in the X direction.
The driving force for moving the Y stage 54 in the Y direction is generated by a linear motor attached to the platen 55. A stator 51e of this linear motor has a coil. A magnet 54c as a movable element of the linear motor is attached to the end portion of a connecting plate 54d connected to the beam 54b of the Y stage 54. When an electric current is allowed to flow through the coil, the magnet generates a driving force in the Y direction. As described above, the Y stage 54 can move along the side surface of a fixed Y guide 52 fixed on the platen 55. The Y-direction driving force is given via an X-direction guiding portion by using the side surface of the beam 54b as a reference surface. An air pad is also used in this X-direction guiding portion.
A cylindrical fixed member 202 and guiding member 203 shown in FIG. 11 correspond to a mechanism which transmits, to the top plate 31, the driving force for moving the X stage 32 shown in FIG. 9 in the X and Y directions. The fixed member 202 and guiding member 203 are guided in a non-contact state by air, and the forces are transmitted to these members via air. By the transmission of these forces, a wafer can be moved to a target position.
The θZT driving mechanism 200 shown in FIG. 11 will be explained below. A base 151 is placed on the X stage 51 shown in FIG. 10. The base 151 has the cylindrical fixed member 202. A porous pad 207 held by the fixed member 202 supports, in a non-contact state, the inner circumferential surface of the guiding member 203 attached to a top plate 204 which is equivalent to the top plate 31 shown in FIG. 9 and holds a wafer and wafer chuck (not shown). The top plate 204 can rotate around the central axis of a θ linear motor (not shown) mounted on the base 151, and can also move up and down in FIG. 11 by Z linear motors 215a equally spaced in the circumferential direction.
To move the top plate on which a substrate such as a wafer is mounted to predetermined X- and Y-coordinates, the conventional alignment apparatus moves the base in the X and Y directions by the X-Y stage while controlling the X- and Y-coordinates of the top plate by using laser interferometers. The top plate is moved to the predetermined position by receiving the driving forces from the base via an air film of a radial air bearing. Although the top plate and base desirably move together, the driving force which the top plate as a holding plate receives produces a phase delay, with respect to the movement of the base, by the contraction of the air film of the hydrostatic bearing.
Instead of this radial air bearing, therefore, a Lorentz force actuator (linear motor) used in the θZT driving mechanism can be used as an X-Y driving mechanism. However, a Lorentz force actuator (linear motor) capable of generating a force which can withstand the weight and acceleration of the top plate and the wafer and wafer chuck mounted on the top plate is large. This makes it difficult to satisfy a motor size (downsizing) and motor heat generation (low heat generation) at the same time.
By contrast, Japanese Patent Application Laid-Open No. 2003-022960 discloses an electromagnetic actuator using an electromagnet, as an actuator which can withstand acceleration and generates little heat.
Unfortunately, this electromagnetic actuator using an electromagnet has an iron core formed by stacking silicon steel plates as electromagnetic steel plates, and thereby has the problem that cut portions formed when the electromagnetic steel plates are processed are rusted. This rust contaminates wafers.
Also, in an electromagnetic actuator using an electromagnet in a vacuum environment, varnish (having the effect of adhesion) is used to adhere the individual silicon steel plates. As shown in FIG. 13, however, this varnish generates a large amount of gases. In a step-and-scan type scanning projection aligner using EUV (Extreme Ultra Violet) light as exposure illuminating light, hydrocarbon (—CH) contained in the gases blurs a mirror and decreases the reflectance of the mirror. As a consequence, the necessary exposure amount can be obtained no longer, and the productivity of micropatterning of semiconductor elements lowers.
In addition, to realize a high productivity, a wafer must be moved at a high speed, and this requires a large acceleration. To apply a large acceleration to the top plate 204 of the θZT driving mechanism 200 shown in FIG. 11, a large acceleration must also be transmitted to the base 151. To this end, it is necessary to raise, for example, the driving force of the Y linear motor 41 shown in FIG. 9. The increased driving force is transmitted to the X stage having the base 151 via the X guide 33. If an air guide is used, similar to the air guide of the θZT driving mechanism 200 as described above, a phase delay is produced by the contraction of the air film of the hydrostatic bearing, so the top plate and base cannot move together. Furthermore, since the accelerating force is large, the supporting force of the air guide becomes smaller than this accelerating force. This makes the air guide unable to function as a guide any longer.
When a large acceleration is necessary, therefore, it is possible to use an electromagnetic actuator which withstands acceleration, generates little heat, and has an iron core formed by stacking electromagnets, similar to the θZT driving mechanism. However, this electromagnetic actuator still has the problems of rust formed on the cut portion of the guide surface of the iron core and gases generated from varnish for fixing the electromagnets.